Attempts have been made to propagate PSV2gpt vector containing hepatitis B virus genome or part thereof--at the Bam H1 integration site--in E. coli. The mechanism of DNA transfection in mammalian cells, including human, has been studied to develop new approaches to increase the rate of transfection. Short exposure to 15% glycerol of 5% DMSO 24 hrs after addition of pSV2gpt DNA to mouse 3T6 cells followed by X-ray treatment at 48 hrs significantly increased uptake and integration of DNA. Transfection of KD cells required a more refined protocol. Treatment of PLC/5 cells with chemical carcinogens increased the production of hepatitis B surface antigen (HBsAg) in a dose-dependent manner without a concommitant increase in HBV DNA content. Repeated treatment of PLC/5 with N-methyl-N'nitro-N-nitrosoguanidine (MNNG) resulted in a cell population with increased production of HBsAg and changed morphological features. These cells had a finite lifespan.